A virtual tape library (VTL) virtually executes a tape drive on a disk device and makes the tape drive seem to be connected to a host device, such as a host computer (for example, see the following Patent LITERATURE 1). In the virtual tape library technique, data is written in a block unit to the disk device.
The virtual tape library can be easily introduced, without a great change in the operation of the physical tape library according to the related art, and can increase, for example, the speed of a backup process.
In addition, a system (virtual tape library system) provided with the virtual tape library includes, for example, a disk array device and uses the disk array device as a cache disk. The system has a structure which virtualizes a tape volume and emulates the tape volume on the cache disk. In general, in the virtual library system, a logical volume is stored in a high-capacity physical medium (virtual library medium), such as a tape, and is operated.
In the virtual tape library system, an export function and an import function have been known as a structure which discharges a stored logical volume and stores the logical volume in an external storage device (for example, see the following Patent LITERATURE 2).
The export function copies a plurality of logical volumes stored in the virtual library system to a physical medium (external storage medium) for external storage. The copied physical medium can be removed to the outside and then used. The import function restores the logical volume from the external storage medium removed to the outside of the virtual library system by the export function to another virtual library system.
In the export function, when the logical volume is copied to the external storage medium, a designated logical volume is copied (recalled) from the virtual library medium to the cache disk. Then, a target logical volume is stored (exported) from the cache disk to the external storage medium.
On the other hand, in the import function, when the logical volume is restored from the external storage medium, a designated logical volume is stored from the external storage medium to the cache disk. Then, the logical volume on the cache disk is stored (migrated to) in the virtual library medium.    [Patent LITERATURE 1] Japanese Laid-open Patent Publication No. 2005-122433    [Patent LITERATURE 2] Japanese Laid-open Patent Publication No. 2009-043162
However, in the virtual tape library system according to the related art, when a large number of logical volume groups need to be exported and imported by data migration at a time, it takes a lot of time to copy and restore data.